▲ The Great Flood in Nepal
Attention is focusing on the cause of a sudden, massive flood in the mountainous Himalayan region of Nepal near the Chinese border that has resulted in heavy casualties.
While the Nepalese government initially presumed the disaster was triggered by an earthquake, experts have raised the possibility that massive glaciers and rock formations collapsed due to climate change in the Himalayas driven by global warming, leading to the catastrophic event.
According to AFP, Reuters, and other news agencies on the 27th local time, the large-scale flood that struck the Bagmati Province in north-central Nepal the previous morning has left 157 people dead and 484 missing, including 391 foreign nationals.
Communication has also been lost with nine South Korean nationals affiliated with Korea South-East Power Co. (KOEN) and Doosan Enerbility who were constructing a hydroelectric power plant in the region.
In Gyirong County, Xigaze, in China's Tibet Autonomous Region near the Nepalese border, a landslide believed to be linked to the cause of this flood occurred the previous morning, leaving 3 people dead and 265 missing.
The previous day, the Nepalese government stated based on preliminary findings that an earthquake in Tibet had triggered the glacier collapse, causing the flood.
Nepalese Foreign Minister Arzu Rana Deuba explained in parliament that an earthquake occurred at around 8:37 AM, followed by reports of a flash flood three minutes later, and added that a massive landslide had blocked the flow of the local Bhote Koshi River.
This raised the possibility that debris and rocks from the landslide blocked the Bhote Koshi River before suddenly giving way, causing muddy water to violently gush downstream.
The U.S. Geological Survey (USGS) also initially stated that a magnitude 4.4 earthquake had struck in Tibet about 47 kilometers north of Rasuwa in Bagmati Province, but later issued a revised report correcting this.
The USGS explained, "Additional analysis of long-period seismic waves and satellite imagery shows that the seismic energy (which was closer to a magnitude 5.2) was actually generated by the landslide," adding, "No earthquake occurred."
The analysis suggests that an earthquake-like shock occurred during the process of massive glaciers and rock crumbling, after which the glacial collapse and debris flow swept downstream, causing the major flood.
Weather experts analyzed that climate change in the Himalayas has continuously increased the likelihood of major disasters like this one.
In the Himalayas, a major water source for approximately 2 billion people in Asia, glaciers have been melting at a rate more than twice as fast in the 21st century due to warming.
Surveys show that the thickness of glaciers in this region decreased by an annual average of 34 centimeters prior to 2000, but has decreased by more than double that rate, at 73 centimeters per year, since 2000.
Climate experts from the International Centre for Integrated Mountain Development (ICIMOD), headquartered in Kathmandu, Nepal, diagnosed that an avalanche originating from a glacier was likely the cause of this flash flood as well.
An ICIMOD expert explained, "The cause was a situation where ice and rocks originating from the glacier on the Nepalese side blocked the river, unleashing a sudden surge of water downstream."
This is also linked to the possibility of floods caused by glacial lake outburst floods (GLOFs).
A glacial lake outburst flood is a phenomenon where a vast amount of water is suddenly released from a lake formed by melting glaciers.
Mountain glaciers are indeed shrinking worldwide due to rising temperatures.
Water from melted glaciers can form glacial lakes, and the number and size of glacial lakes have been increasing since the 1990s.
Floods occur when these so-called "natural dams" made of ice and rock holding back the lakes suddenly collapse.
Experts expect such floods to increase in the future due to climate change.
In July of last year, a large-scale landslide and flood also occurred in the Gyirong Kouan area of Gyirong County, Xigaze, Tibet—where the landslide also struck this time—leaving 1 person dead and 28 missing across both Nepal and Tibet.
Satellite imagery analysis conducted by Chinese authorities after last year's disaster revealed that 55 glacial lakes were distributed upstream of the accident site.
The total area of these glacial lakes reached 3.39 square kilometers.
Experts analyzed that last year's flood was also caused by a sudden drainage of water from lakes on the glacier surface.
Hatim Sharif, a hydrologist at the University of Texas at San Antonio, pointed out that it is also striking that there was almost no rainfall before this flood occurred.
He noted, "This is a case that essentially exposes the limitations of virtually every flood warning system in the world."
Because "flood warnings" based on rainfall amounts do not go off, residents downstream have no time to evacuate, he explained.
He emphasized that the massive wall of muddy water rushing down at high speeds in mountainous terrain forms a deadly combination resembling liquid concrete, making it useless to spot it and try to run away, meaning the only solution is to climb onto a hill 6 meters high.
The "V"-shaped gorges of the Himalayan mountains, down which soil and muddy water rushed at very high speeds, were also pointed out as a contributing factor that amplified casualties.
Dorothy Heinrich, a researcher at the University of Reading in the UK, explained, "In mountainous terrain, rivers can narrow significantly in certain sections. (When the river is blocked by an avalanche or landslide,) a large volume of water builds up, and (when it suddenly bursts,) it causes a flood of unbelievable speed."
With search and rescue operations for the missing hindered by massive amounts of debris and rugged terrain, concerns have also been raised that a "secondary flood" could occur.
An ICIMOD official stated, "Blockages still remain in the upper reaches of the river along the Nepal-China border," adding, "Authorities are warning that a second flood could occur."
(Photo: Yonhap News)
(Reported by Kim Young-a)
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